1. Field of the Invention
The present invention relates to an improved apparatus for spraying powder circumferentially around a pipe joint. More particularly, this invention relates to improvements in the powder fluidization chamber and in the means for supplying the air powder suspension to the weld joint.
2. Prior Art
In the above co-pending application, there is described a system for spraying or dispensing a powdered material circumferentially around a pipe. The pipe itself is made up from pipe sections which have been previously coated at the mill except for the ends thereof which are left uncoated so that the sections can be welded together in the field in end-to-end relation. The apparatus of the aforementioned co-pending application, therefore, deposits powder on the weld joints (which have been previously heated) to complete the coating of the pipe.
However, the use of the Venturis (in the above application) to draw the fluidized powder out of the powder suspension device and deliver it to the weld joint requires the use of an air compressor. As well as the problems which accompany moist air from the compressor being in contact with the powder, additional problems due to the rapid wearing of the Venturi components have been encountered.
Even with the use of the Venturis, it is difficult to meter exactly the quantity of powder to be supplied to each weld joint. Obviously, an insufficient quantity of powder will result in a poor coating of the weld. The present invention provides a system which is operator-adjustable thereby allowing a desired metered amount of powder to be delivered rather than relying on the Venturis in which delivery of powder is dependent upon component wear.
The apparatus of the aforementioned application requires a filtering medium, such as a cloth bag, for use in conjunction with the powder return housing or device. Since the cloth bag in necessarily porous, accidental or incidental leakage of powder from the bag, can result in contamination of the air around the apparatus and it can also result in loss of powder from the system. The present invention provides a means for returning excess powder from the pipe joint and yet eliminating the porous filter bag and its attendent problems.